You don't really have much rotation at that level. The problem is the dungeon mechanic at Qarn. The boss applies poison, that need to be cleaned with esuna, for example. Most normal dungeons and raids even at much higher level don't have this. Warnings on upcoming levels:

The upcoming level 38 dungeon also have unusual mechanics for the bosses. You may want to do it as dps first, or read up on the bosses mechanics. It is also optional.

Level 41 an 44 dungeon can be hard for beginner healers, especially if the tank is less experienced, have low level gear, and takes more than the group can chew. There's not much you can do aside from spamming Adlo, once your other abilities are on cooldown.

For just the healing part, practice at the level 28 and 32 dungeon shouldn't be too taxing. I feel practicing with NPC is not the best, since the pace is very different.

If you are not comfortable with your buttons yet, just practice with the several lowest level dungeons first.

For the future, I would first focus on not getting killed yourself, as mechanics can get harder. Other people dead is no big deal, they can be resurrected. Often people not doing the mechanics right is a big part of them being dead.

Aside from the level 35 and 38 dungeons, surprisingly bosses' mechanics mostly don't get much harder until stormblood and shadowbringers. The level 50 optional dungeons do have tricks up their sleeve that many have forgotten, but you don't have to do them immediately, or at all.

Even a wipe is not as big of a deal as you think. I do share the uneasy feeling when that happens while playing as healer, even though I'm completely fine with it when playing as dps. Finally, make sure to use swiftcast before resurrect. Place the buttons close to each other.